You can add a new field to a contact form by creating your own custom field in Settings › Custom Fields. You'll then see that new custom field as an option on your Contact Form Field Configuration.

For example, here's a new custom field created to capture more information about how the couple met:

This can now be selected as a field on the Contact Form:

You can choose to make this field required or optional, and also change the label to different wording if you'd like to.

The information put into those fields will not map to any other existing fields on the lead that is created in Táve, but they will appear in your new lead email notification and in the appropriate custom field on the lead's worksheet: